How do I modify the Data Frame Extents from an ArcObjects application

We're upgrading to ArcGIS 10 and we are changing a number of our feature classes and databases. To assist our 2500 users we have written a program that converts old layers to the new layers where possible keeping the symbology etc.

I need a little help in accessing the data frames associated with a map and changing the maximum extent when users click on the zoom out to full extent icon. Going through the object models can be quite a chore.

///<summary>///Set the extent of the ActiveView to be the maximum extent of a SpatialDomain. ///</summary>///<param name="spatialReference">An ESRI.ArcGIS.Geometry.ISpatialReference interface that is the input SpatialDomain.</param>///<param name="activeView">An ESRI.ArcGIS.Carto.IActiveView interface that is the ActiveView for which to recieve the new extent.</param>///<remarks></remarks>public void SetMaxExtentOnSpatialDomain(ESRI.ArcGIS.Geometry.ISpatialReference spatialReference, ESRI.ArcGIS.Carto.IActiveView activeView){